1. Field of the Invention
The present invention relates to improvements of an in-vehicle engine control apparatus in which multiple fuel injections, i.e. fuel injections of plural times are performed to the same cylinder in one combustion cycle period of an internal combustion engine, and in particular to an in-vehicle engine control apparatus in which a temperature rise of a fuel injection control portion following such multiple fuel injections is suppressed.
2. Description of the Related Art
A fuel injection type multi-cylinder engine includes a collective injection type which performs the fuel injection once in one combustion cycle period of each cylinder, a split (divided) injection type which performs the fuel injection of the same amount as a whole by multiple split injections, or an intermittent split type which alternately repeats the collective injection and the split injection, in order to improve vehicle exhaust emission measures and fuel efficiency depending on the load condition.
It is to be noted that split injection mentioned herein includes a variety of injection types, for example from a split injection type of two steps or stages composed of a former injection in the inlet stroke and a latter injection in the compression stroke to a split injection type of five steps at maximum composed of a pilot injection in the compression stroke; a pre-injection, a main injection, and an after-injection in the explosion stroke; and a post injection in the exhaust stroke.
For instance, “Fuel injection control apparatus” of Japanese Patent Laid-Open Publication 2005-337038 (hereafter, referred to as Patent Document 1) is, as shown in FIGS. 3, 4, and 8) provided with a thermistor 41 for detecting an ambient temperature Ta of FETs 35-37 between the charging FET 35 (boosting switch element mentioned in this patent application) for generating a boosted high voltage, the separating FET 36 (rapid excitation switch element mentioned in this patent application) for applying a boosted high voltage to a plurality of injectors 20, and the constant current FET 37 (power feeding-sustaining switch element mentioned this patent application) for feeding power to the injectors 20 from a battery power supply. In addition, a temperature difference between the ambient temperature Ta and a junction temperature Tj of the FETs 35-37 when operated on the severest condition is preliminarily calculated and stored, which is added this to the actual ambient temperature Ta, thereby calculating the maximum junction temperature Tjmax. When this exceeds a predetermined temperature (e.g. 150 degrees C.) for determining an overheat state, the number of split step (five steps at maximum) of the split injection is reduced, thereby suppressing such a temperature rise.
According to FIG. 10 and the descriptions of Paras. [0055], [0056], it is described that the thermistor 41 is preferably provided in close vicinity of a heatsink of MOSFET, that is a part to be measured, to measure the ambient temperature Ta at the nearest position, thereby reducing a calculation error of the junction temperature.
In the descriptions, four cylinder FETs (rapid cutoff switch element mentioned in this patent application) for four cylinder engine, four separating FETs 36 (rapid excitation switch element mentioned in this patent application), two constant current FETs 37 (power feeding-sustaining switch element mentioned in this patent application) by cylinder group, and two charging FETs 35 (boosting switch element mentioned in this patent application) for each cylinder group are used.
While two separating FETs 36 and one charging FET 35 are generally used, Patent Document 1 uses four separating FETs 36 and two charging FETs 35 to disperse the heat generated, where a connecting circuit arrangement of the four separating FETs 36 and the two charging FETs 35 is not disclosed.
Also, Japanese Patent Laid-Open Publication 2011-220244 (hereafter, referred to as Patent Document 2) describes “Fuel injection control apparatus” in FIG. 4 such that based on the in-apparatus temperature T detected by the thermistor or the engine rotational speed N, all of injection controls A-D are allowed to be performed when the detected temperature is equal to or less than T11 or the rotational speed is equal to or less than N11; either the control B or the control D which is larger in the heat generation amount is allowed to be performed when the detected temperature is between T1−T12 (T12>T11) or the rotational speed is between N11−N12 (N12>N11); or only the control A and the control C are allowed to be performed with the control B and the control D prohibited to be performed when the detected temperature exceeds T12 or the rotational speed exceeds N12, for suppressing the in-apparatus temperature.
The control A mentioned therein is a fuel injection control having a long valve opening command period which includes a rapid power feeding period of a large current and a valve opening-holding period of a small current as shown in FIG. 2(A), and the control B is a fuel injection control having a short valve opening command period which includes only a rapid power feeding period of a large current as shown in FIG. 2(B).
The control C is a fuel injection control enabling a fuel injection once in one combustion cycle period of the engine as shown in FIG. 3(A), and the control D is a fuel injection control enabling the split injection twice as shown in FIG. 3(B).
Para. [0038] of Patent Document 2 describes that the heat amount generated in the injector driving circuit 22 by the control D for performing multiple fuel injections is larger than that by the control C as is obvious.
Para. [0036] of Patent Document 2 describes that the heat amount generated in the injector driving circuit 22 by the control B which cuts off a large current is larger than that by the control A.
However, the valve opening command period for the injector increases in proportion to the inlet air amount responsive to the depressing degree of acceleration pedal and decreases in reverse proportion to the engine rotational speed. Therefore, in case where the fuel injection amount required is small, requiring no valve opening-holding period, and the power feeding is stopped immediately after the rapid power feeding current has attenuated, the heat amount generated in the injector driving circuit 22 by the control B is apparently smaller than that by control A, so that it is not simply possible to specify what level of attenuation cutoff current would make the control B more disadvantageous.
Since even though the power feeding is stopped during the rapid power feeding period of a large current, the generated heat amount will not increase if the attenuation is made by a commutation circuit or power is collected by a capacitor, generally there is a contradiction that it cannot be said that the generated heat amount by the control B is simply larger than that by the control A.
Also, “Driving apparatus for electromagnetic load” of Japanese Patent Laid-Open Publication 2001-14043 (hereafter, referred to as Patent Document 3) related to the thermal control according to this patent application comprises, as shown in FIG. 1, a boosting circuit mainly composed of an inductor L11, a transistor T00, an oscillating circuit 100, and capacitors C10, C20 for rapidly exciting injector solenoids 101a-104a. This apparatus is disclosed as one example of a regenerative charging system in which the counter electromotive force energy generated in the solenoids 101a-104a at the time of electrical conduction cutoff is collected by diodes D10-D40 and accumulated by the capacitors C10, C20 for the reduction of power loss, where ECU 200 is adapted to monitor the voltage of the capacitors C10, C20 at the time of electrical conduction cutoff of the solenoids 101a-104a and adjust the electrical conduction cutoff timing even though the voltage is varied, thereby stabilizing the valve opening characteristics.
(1) Explanation of Prior Art Problem
“Fuel injection control apparatus” according to the above Patent Document 1 is provided with the thermistor 41 for detecting the ambient temperature Ta at the nearest position of the FET that is a switch element to be thermally monitored and restricts the number of injection steps or stages so that the junction temperature of the switch element which is estimated from the ambient temperature Ta may become a predetermined temperature or less.
However, the fuel injection control apparatus is generally installed in the engine room, so that it is necessary to assume the temperature inside the engine room to be 120 degrees C. at the maximum while in order to make the temperature of the junction portion of the semiconductor element below e.g. 175 degrees C. or less, it is necessary to control the temperature of the heatsink portion representing the inside temperature of the semiconductor element to 150 degrees C. or less.
Therefore, there is a problem that the internal temperature rise allowed for the switch element in the inside of the fuel injection control apparatus becomes 20-30 degrees C. or less, and that even though the temperature at the nearest position of the switch element is detected, its distribution between the environmental temperature and the temperature rise due to the self-heat generation is not detected, so that the temperature rise component of the switch element cannot be accurately controlled, and that even if the temperature rise is actually much smaller, a control only with a margin based on the highest temperature rise for the worst condition scenario.
It is to be noted that Patent Document 1 is adapted to disperse the generated heat by using the four separating FETs 36 (rapid excitation switch element mentioned in this patent application), and that for this purpose, it is necessary to connect eight positive and negative terminals in total of the four solenoids 101a-104a to the driving circuit 100. Therefore, there is a problem that the cost and the vehicle weight increase as the number of external wiring increases, and that the contact reliability is lowered due to the increase of pin number of connector, and an occurrence probability of disconnection/short-circuit a ground fault contacting the ground circuit of external wirings, or an abnormal sky fault connection thereof with the positive side wiring of the power supply grows.
Also, in “Fuel injection control apparatus” according to the above Patent Document 2, thermal information acquiring means that indicates the thermal sensor or the engine rotational speed used therein is not specified as to acquiring the temperature of which portion in the inside of the fuel injection control apparatus and which switch element in the driving circuit is focused is not specified as well.
Therefore, there is a problem that while if the engine rotational speed is assumed to be acquired by thermal information acquiring means, the temperature rise of e.g. the boosting switch element can be estimated from the engine rotational speed, but the temperature of the boosting switch element itself cannot be estimated if the environmental temperature is not known.
Also, there is a problem that even though the engine rotational speed is determined, the temperature rise itself of the switch element which supplies the valve opening-holding current cannot be estimated.
Also, there is a problem that if the thermal sensor is made a thermal information acquiring means and if the thermal sensor detects the temperature of the nearest position of the heat generated element, the distinction between the environmental temperature and the temperature rise due to the self-generated heat cannot be made, so that if it is provided at a position far from the heat generated element, the temperature of the heat generated element itself cannot be estimated.
While FIG. 5 of Patent Document 2 determines an applicable control mode with a dual map of the detected temperature by the thermal sensor and the engine rotational speed upon attending to the above problem, a plurality of switch elements in the driving circuits are not individually focused, so that individual accurate determination cannot be made and only a general determination having a certain margin can be done.
On the other hand, there is a problem that in “Driving apparatus of electromagnetic load” according to the above Patent Document 3, the number of use of the power feeding-sustaining switch elements T11, T21, the rapid excitation switch elements T12, T22, and the boosting switch element 100 is fewer than the number of use of the rapid cutoff switch elements T10-T40, sharing a plurality of solenoids, so that the power loss is concentrated and the temperature rise of the local part becomes excessive.
Also, there is a problem that while the regenerative charging system for suppressing the temperature rise of the rapid cutoff switch elements T10-T40 and the boosting switch element T100 is applied, complicated adjusting means for stabilizing the valve opening characteristics is required.
Also, as seen from FIG. 2, since the transistors T13, T23 in the boosting circuit are connected by cylinder group, the capacitors C10, C20 cannot be alternately used with the same solenoid, resulting in the arrangement of concentrating the generated heat to the single boosting element T100 and the single inductor L11.